If you experienced "Transaction is too big" when using Ledger to send NEO or GAS assets. It's likely that you have too many UTXOs. Ledger can only handle a limited amount of data sent to its device.
Send smaller amount to yourself. It will help reduce number of UTXOs.
What is UTXO Manager?
Connect a wallet to see how many UTXO for each asset. This app will help you combine those UTXOs. Ideally, There should be only 1 UTXO for each asset.